--- title: "Skincare Glossary — School of Dermatology" url: https://schoolofdermatology.com/glossary description: "A comprehensive glossary of skincare and dermatology terms explained in plain English. From AHA to Zinc Oxide, understand every ingredient and concept." lang: en --- # Skincare Glossary Every skincare and dermatology term you need to know, explained in plain English. ## A AHA (Alpha Hydroxy Acid) (https://schoolofdermatology.com/glossary/aha-alpha-hydroxy-acid) — Alpha hydroxy acids are a group of water-soluble acids derived from fruits, milk, and sugar cane. The most common AHAs i… Antioxidant (https://schoolofdermatology.com/glossary/antioxidant) — Antioxidants are molecules that protect the skin from damage caused by free radicals — unstable atoms generated by UV ra… Astringent (https://schoolofdermatology.com/glossary/astringent) — An astringent is a topical product or ingredient that causes the contraction of skin cells and tissues, temporarily tigh… Atopic Dermatitis (https://schoolofdermatology.com/glossary/atopic-dermatitis) — Atopic dermatitis is a chronic, inflammatory skin condition and the most common form of eczema. It causes dry, itchy, re… ## B Barrier Function (https://schoolofdermatology.com/glossary/barrier-function) — The skin's barrier function refers to the protective role of the outermost layer of the epidermis, the stratum corneum. … BHA (Beta Hydroxy Acid) (https://schoolofdermatology.com/glossary/bha-beta-hydroxy-acid) — Beta hydroxy acid refers primarily to salicylic acid, an oil-soluble exfoliant that penetrates into pores to dissolve ex… Broad Spectrum (https://schoolofdermatology.com/glossary/broad-spectrum) — Broad spectrum is a sunscreen classification indicating that a product protects against both UVA and UVB rays. UVB rays … ## C Ceramides (https://schoolofdermatology.com/glossary/ceramides) — Ceramides are a family of waxy lipid molecules that occur naturally in the skin and make up about 50% of the lipids in t… Chemical Exfoliant (https://schoolofdermatology.com/glossary/chemical-exfoliant) — A chemical exfoliant is a skincare product that uses acids or enzymes to dissolve the bonds between dead skin cells, pro… Collagen (https://schoolofdermatology.com/glossary/collagen) — Collagen is the most abundant protein in the human body, providing structural support to the skin, bones, tendons, and l… Comedogenic (https://schoolofdermatology.com/glossary/comedogenic) — Comedogenic describes an ingredient or product that has a tendency to clog pores and contribute to the formation of come… Comedone (https://schoolofdermatology.com/glossary/comedone) — A comedone is a basic acne lesion formed when a hair follicle becomes clogged with dead skin cells, sebum, and sometimes… Contact Dermatitis (https://schoolofdermatology.com/glossary/contact-dermatitis) — Contact dermatitis is a localized skin inflammation that occurs when the skin comes into direct contact with a substance… Cystic Acne (https://schoolofdermatology.com/glossary/cystic-acne) — Cystic acne is the most severe form of acne, characterized by large, deep, painful, inflamed breakouts that form beneath… ## D Dermatitis (https://schoolofdermatology.com/glossary/dermatitis) — Dermatitis is a general term for skin inflammation, characterized by redness, swelling, itching, and sometimes blisterin… Dermis (https://schoolofdermatology.com/glossary/dermis) — The dermis is the thick middle layer of the skin, located between the epidermis (outer layer) and the hypodermis (subcut… Desquamation (https://schoolofdermatology.com/glossary/desquamation) — Desquamation is the natural, ongoing process by which the outermost layer of dead skin cells (corneocytes) sheds from th… Double Cleansing (https://schoolofdermatology.com/glossary/double-cleansing) — Double cleansing is a two-step face washing method that originated in Korean and Japanese skincare routines. The first s… ## E Elastin (https://schoolofdermatology.com/glossary/elastin) — Elastin is a highly elastic protein found in the dermis that allows the skin to stretch and snap back to its original sh… Emollient (https://schoolofdermatology.com/glossary/emollient) — An emollient is a type of moisturizing ingredient or product that works by filling in the gaps between skin cells with l… Emulsifier (https://schoolofdermatology.com/glossary/emulsifier) — An emulsifier is an ingredient that allows two normally immiscible substances — typically oil and water — to mix togethe… Enzymes (https://schoolofdermatology.com/glossary/enzymes) — In skincare, enzymes are biological proteins used as gentle exfoliating agents. They work by breaking down the keratin p… Epidermis (https://schoolofdermatology.com/glossary/epidermis) — The epidermis is the outermost layer of the skin and serves as the body's primary physical barrier against the environme… Exfoliation (https://schoolofdermatology.com/glossary/exfoliation) — Exfoliation is the process of removing dead skin cells from the surface of the skin to reveal fresher, smoother skin ben… ## F Fibroblast (https://schoolofdermatology.com/glossary/fibroblast) — Fibroblasts are the primary cells in the dermis responsible for producing collagen, elastin, glycosaminoglycans (like hy… Fitzpatrick Scale (https://schoolofdermatology.com/glossary/fitzpatrick-scale) — The Fitzpatrick Scale is a numerical classification system developed by dermatologist Thomas Fitzpatrick in 1975 that ca… Free Radicals (https://schoolofdermatology.com/glossary/free-radicals) — Free radicals are unstable, reactive molecules with unpaired electrons that damage cells by stealing electrons from othe… ## G Glycerin (https://schoolofdermatology.com/glossary/glycerin) — Glycerin (also called glycerol) is one of the most effective and widely used humectant ingredients in skincare. It is a … Glycolic Acid (https://schoolofdermatology.com/glossary/glycolic-acid) — Glycolic acid is the smallest and most widely researched alpha hydroxy acid (AHA), derived from sugar cane. Its small mo… ## H Humectant (https://schoolofdermatology.com/glossary/humectant) — A humectant is a type of moisturizing ingredient that attracts and binds water molecules from the environment and from d… Hyaluronic Acid (https://schoolofdermatology.com/glossary/hyaluronic-acid) — Hyaluronic acid (HA) is a naturally occurring glycosaminoglycan found throughout the body's connective tissues, with the… Hyperpigmentation (https://schoolofdermatology.com/glossary/hyperpigmentation) — Hyperpigmentation is a common skin condition where patches of skin become darker than the surrounding areas due to exces… Hypodermis (https://schoolofdermatology.com/glossary/hypodermis) — The hypodermis, also called the subcutaneous layer or subcutis, is the deepest layer of the skin lying below the dermis.… ## I Inflammation (https://schoolofdermatology.com/glossary/inflammation) — Inflammation is the immune system's response to injury, infection, or irritation, characterized by redness, swelling, he… Irritant (https://schoolofdermatology.com/glossary/irritant) — An irritant is any substance that causes a non-allergic inflammatory reaction when it comes into contact with the skin. … ## J Jojoba Oil (https://schoolofdermatology.com/glossary/jojoba-oil) — Jojoba oil is a liquid wax ester extracted from the seeds of the jojoba plant (Simmondsia chinensis), native to the sout… ## K Keratin (https://schoolofdermatology.com/glossary/keratin) — Keratin is a tough, fibrous structural protein that is the primary component of the outermost layer of skin (stratum cor… Keratinocyte (https://schoolofdermatology.com/glossary/keratinocyte) — Keratinocytes are the predominant cell type in the epidermis, making up approximately 90% of epidermal cells. They are p… ## L Lactic Acid (https://schoolofdermatology.com/glossary/lactic-acid) — Lactic acid is an alpha hydroxy acid (AHA) derived from milk that serves as a gentle chemical exfoliant. It has a larger… LED (Light Emitting Diode) (https://schoolofdermatology.com/glossary/led-light-emitting-diode) — In skincare, LED refers to light emitting diode technology used to deliver specific wavelengths of light to the skin. Di… Lipid Barrier (https://schoolofdermatology.com/glossary/lipid-barrier) — The lipid barrier (also called the lipid matrix or lipid bilayer) is the intercellular 'mortar' between the corneocytes … ## M Melanin (https://schoolofdermatology.com/glossary/melanin) — Melanin is the natural pigment produced by melanocytes in the basal layer of the epidermis that gives skin, hair, and ey… Melanocyte (https://schoolofdermatology.com/glossary/melanocyte) — Melanocytes are specialized cells located in the basal layer of the epidermis that produce melanin, the pigment responsi… Microbiome (https://schoolofdermatology.com/glossary/microbiome) — The skin microbiome refers to the vast community of microorganisms — including bacteria, fungi, viruses, and mites — tha… Milia (https://schoolofdermatology.com/glossary/milia) — Milia are small, white or yellowish, dome-shaped bumps that appear on the skin when keratin (a protein) becomes trapped … Moisturizer (https://schoolofdermatology.com/glossary/moisturizer) — A moisturizer is a skincare product designed to hydrate the skin and prevent water loss by combining three types of mois… ## N Niacinamide (https://schoolofdermatology.com/glossary/niacinamide) — Niacinamide (also known as nicotinamide) is a form of vitamin B3 that has become one of the most versatile and popular a… Non-Comedogenic (https://schoolofdermatology.com/glossary/non-comedogenic) — Non-comedogenic is a term used to describe skincare and cosmetic products that are formulated to be less likely to clog … ## O Occlusives (https://schoolofdermatology.com/glossary/occlusives) — Occlusives are a category of moisturizing ingredients that work by forming a physical barrier on the skin's surface to p… Oxidative Stress (https://schoolofdermatology.com/glossary/oxidative-stress) — Oxidative stress occurs when there is an imbalance between the production of free radicals (reactive oxygen species) and… ## P Peptides (https://schoolofdermatology.com/glossary/peptides) — Peptides are short chains of amino acids (typically 2-50 amino acids long) that serve as building blocks for proteins li… pH Balance (https://schoolofdermatology.com/glossary/ph-balance) — pH (potential of hydrogen) is a measure of acidity or alkalinity on a scale of 0 to 14, with 7 being neutral. Healthy sk… Photobiomodulation (https://schoolofdermatology.com/glossary/photobiomodulation) — Photobiomodulation is the use of specific wavelengths of light — typically red and near-infrared — to stimulate cellular… PIE (Post-Inflammatory Erythema) (https://schoolofdermatology.com/glossary/pie-post-inflammatory-erythema) — Post-inflammatory erythema (PIE) refers to the flat, pink to red or purple marks left on the skin after an inflammatory … PIH (Post-Inflammatory Hyperpigmentation) (https://schoolofdermatology.com/glossary/pih-post-inflammatory-hyperpigmentation) — Post-inflammatory hyperpigmentation (PIH) is a type of hyperpigmentation that occurs as the skin heals from inflammation… Pore (https://schoolofdermatology.com/glossary/pore) — Pores are the tiny openings on the skin's surface through which hair follicles reach the surface and through which sebum… Propolis (https://schoolofdermatology.com/glossary/propolis) — Propolis is a natural, resinous substance produced by honeybees from tree buds, sap flows, and other botanical sources. … ## R Red Light Therapy (https://schoolofdermatology.com/glossary/red-light-therapy) — Red light therapy uses wavelengths between 620-700 nanometers to penetrate the skin and stimulate mitochondrial energy p… Retinoid (https://schoolofdermatology.com/glossary/retinoid) — Retinoids are a class of chemical compounds derived from vitamin A that are widely considered the gold standard in anti-… Retinol (https://schoolofdermatology.com/glossary/retinol) — Retinol is the most popular and widely available over-the-counter form of vitamin A (retinoid) used in skincare. It is a… Rosacea (https://schoolofdermatology.com/glossary/rosacea) — Rosacea is a chronic, inflammatory skin condition that primarily affects the central face — cheeks, nose, chin, and fore… ## S Salicylic Acid (https://schoolofdermatology.com/glossary/salicylic-acid) — Salicylic acid is a beta hydroxy acid (BHA) derived from willow bark that is one of the most effective and widely used i… Sebaceous Gland (https://schoolofdermatology.com/glossary/sebaceous-gland) — Sebaceous glands are small, oil-producing glands attached to hair follicles throughout the body (except on the palms and… Sebum (https://schoolofdermatology.com/glossary/sebum) — Sebum is the waxy, oily substance produced by sebaceous glands to lubricate and waterproof the skin and hair. It is comp… Sensitized Skin (https://schoolofdermatology.com/glossary/sensitized-skin) — Sensitized skin is a condition where the skin has become temporarily reactive, irritated, and easily aggravated due to e… Skin Cycling (https://schoolofdermatology.com/glossary/skin-cycling) — Skin cycling is a skincare method popularized by dermatologist Dr. Whitney Bowe that involves rotating active ingredient… SPF (https://schoolofdermatology.com/glossary/spf) — SPF stands for Sun Protection Factor, a numerical rating that indicates how much longer a sunscreen allows you to stay i… Stratum Corneum (https://schoolofdermatology.com/glossary/stratum-corneum) — The stratum corneum is the outermost sublayer of the epidermis and the body's first physical barrier against the externa… Sunscreen (https://schoolofdermatology.com/glossary/sunscreen) — Sunscreen is a topical product that protects the skin from the harmful effects of ultraviolet (UV) radiation, which caus… ## T Toner (https://schoolofdermatology.com/glossary/toner) — A toner is a liquid skincare product applied after cleansing and before serums and moisturizers. Historically, toners we… Transepidermal Water Loss (TEWL) (https://schoolofdermatology.com/glossary/transepidermal-water-loss-tewl) — Transepidermal water loss (TEWL) is the process by which water passes from the dermis through the epidermis and evaporat… Tretinoin (https://schoolofdermatology.com/glossary/tretinoin) — Tretinoin (all-trans retinoic acid) is the most potent and well-researched prescription retinoid, available under brand … ## U Urea (https://schoolofdermatology.com/glossary/urea) — Urea is a naturally occurring compound found in the skin as part of the natural moisturizing factor (NMF) — the collecti… UVA (https://schoolofdermatology.com/glossary/uva) — UVA (Ultraviolet A) rays are the longest wavelength of ultraviolet radiation (320-400 nm) emitted by the sun. They accou… UVB (https://schoolofdermatology.com/glossary/uvb) — UVB (Ultraviolet B) rays are medium-wavelength ultraviolet radiation (280-320 nm) that primarily affects the epidermis, … ## V Vitamin C (Ascorbic Acid) (https://schoolofdermatology.com/glossary/vitamin-c-ascorbic-acid) — Vitamin C (L-ascorbic acid) is one of the most researched and effective antioxidant ingredients in skincare. It neutrali… Vitamin E (Tocopherol) (https://schoolofdermatology.com/glossary/vitamin-e-tocopherol) — Vitamin E (tocopherol) is a fat-soluble antioxidant that occurs naturally in the skin's sebum and plays a critical role … ## W Whiteheads (https://schoolofdermatology.com/glossary/whiteheads) — Whiteheads (closed comedones) are a type of non-inflammatory acne that appears as small, flesh-colored or white bumps on… Witch Hazel (https://schoolofdermatology.com/glossary/witch-hazel) — Witch hazel is a plant-derived ingredient extracted from the bark and leaves of the Hamamelis virginiana shrub, native t… ## X Xeroderma (https://schoolofdermatology.com/glossary/xeroderma) — Xeroderma is the medical term for abnormally dry skin, characterized by roughness, tightness, flaking, scaling, cracking… ## Z Zinc (topical) (https://schoolofdermatology.com/glossary/zinc-topical) — Topical zinc refers to various zinc compounds used in skincare for their anti-inflammatory, antimicrobial, wound-healing… Zinc Oxide (https://schoolofdermatology.com/glossary/zinc-oxide) — Zinc oxide is a mineral (inorganic) sunscreen ingredient that provides broad-spectrum protection against both UVA and UV… ## Stay Informed. 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